hi there, i used to own an older fiesta, so if the clock is the same as what mine was (digital) then the way to change the time is to turn on the ignition key, then the buttons to change the time should work. also if you press the hour and minute buttons together, it will change between 24 hour, to 12 hour time format. i hope this info is useful for you! good luck.
daniel laker
April 2008